Many recent experiments have studied matter in a new regime, where large numbers of particles exhibits exhibit complex varieties of quantum entanglement. I will describe two such experiments, in magnetic insulators, and in ultracold atoms in optical lattices. In some cases, new insights and powerful computational methods have come from an unexpected source: the methods of gauge-gravity duality drawn from string theory. I will also briefly describe the status of much current research applying these duality methods to novel metallic states of electrons found in the high temperature superconductors.